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Wednesday, 26 March 2014

85 mm U-10

Even though an 85 mm tank gun was not put into production until 1943, experiments with guns of these calibers predate the invasion of the Soviet Union. Before Tigers and Panthers hit Russian land, engineers knew that anti-tank guns must constantly evolve. The U-10 was one such proposed design.

"In addition to my letter #1546s from November 3rd, 1941, I deport that the U-10 divisional gun, created by placing an 85 mm model 1939 gun barrel on a 122 mm model 1938 (M-30) howitzer mount, has been tested at the Ural artillery proving grounds on October 18th, 20th, 21st, and 25th (see report #1998 from the Ural proving grounds in 6161s from November 9th).

Aside from the above trials, the experimental U-10 prototype is undergoing trials by the commission you appointed, led by Military Engineer 2nd grade, comrade Sorokin.

200 shots have been fired from the gun, and it has been towed 300 km by a 3-ton ZiS-5 truck.

Trials showed that:

The precision of the gun gives better results than existing anti-tank and divisional guns.
At 1000 meters, average vertical deviation is 0.2 m, horizontal is 0.17 m.

At 2000 meters, average vertical deviation is 0.35 m, horizontal is 0.42 m

The system is stable when firing from dirt or from concrete.

After 300 km of towing (900 km total), a leaf spring broke. When the system was taken apart, it was discovered that the semi-automatic mechanism casing burst. This could only happen after firing several rounds with a muzzle velocity of 850-860 m/s and maximum chamber pressure of 2850-3000 kg/cm^2 (stock muzzle velocity is 800 m/s and maximum pressure is 2535 kg/cm^2).

The spring was replaced, and the commission continues testing. The system will be towed with a limber by a tractor and a car, as well as a horse.

A broken spring after 900 km of poor, bumpy roads is not a reason to delay the U-10 battery sent to the army according to the GAU KA Chief, Colonel-General of Artillery, comrade Yakovlev.

The issue of reinforcing the spring or including spares will be resolved upon the completion of trials by the current commission.

The 85 mm gun on the M-30 mount (U-10) has many positive qualities, giving it a right to be adopted into divisional artillery. Th U-10 gives the division the ability to combat powerful enemy tanks. Its good stability and gun shield give it an advantage over the 85 mm AA gun. A U-10 gun in a division will be used in its intended role.

The gun's higher mobility caused by its smaller weight, lower time to battle readiness, and same rate of fire as the AA gun allows units greater mobility when fighting tanks.

The U-10 gun is easier to produce than the AA gun, and its production will cause no additional difficulties.

I send you the technical documentation for the U-10 gun, received from the factory in #F-609/63ss on November 23rd of this year. Pending completion of the trails by the commission led by Military Engineer 2nd grade comrade Sorkin, I deem it possible to raise the question of adopting the U-10 to the GKO."

In October of 1941, Uralmash, on its own initiative, produced a new 85 mm U-10 divisional gun.

The new gun is built by placing the oscillating part of the 85 mm model 1939 AA gun on a model 1938 howitzer mount.

The experimental prototype of the U-10 gun underwent gunnery and mobility trials at the Uralmash factory and Ural proving grounds in the presence of Army General comrade. Tulenev and Lieutenant-General comrade Sivkov. Brief information on the results of the trials are included in letter #1546 from November 3rd, 1941 from the regional engineer at UZTM, Military Engineer 1st grade, comrade Firsov. The same letter informs us that according to the orders of comrade Yakovlev, a battery of 4 of these guns is to be sent to the acting army.

According to orders of Major-General comrade Hohlov, the 4 U-10 guns will be sent to base #36 to be assigned to the Chief Quartermaster of Artillery of the Moscow Military District for trials and combat work on the front. At the same time, the Chief Quartermaster was sent a letter #790030 on November 10th, 1941, titled "List of main questions that should be answered after frontline trials of U-10 guns:, confirmed on November 13th by Major-General comrade Hohlov.

On December 9th, 1941, letter #1691ss was received, sent on November 28th, 1941 by the UZTM regional engineer containing trials materials by the commission led by Military Engineer 2nd grade comrade Sorkin. Due to the new re-organization of GAU, I am sending these materials to you. No information has arrived regarding the combat use of the experimental U-10 85 mm guns has arrived at GAU."

As we haveseenbefore, "powerful enemy tanks" failed to materialize, and the gun never reached production. However, the barrel of the 85 mm AA gun returns to a dedicated anti-tank role (much like the Germans, the Soviets used their high caliber AA guns in direct fire roles when necessary) in 1943, when the SU-85, IS-1, and T-34-85 are produced, and then as a divisional D-44 gun in 1944.